Magneto-elastic coupling in La(Fe, Mn, Si)₁₃H<i>y</i> within the Bean-Rodbell model

First order magnetic phase transition materials present a large magnetocaloric effect around the transition temperature, where these materials usually undergo a large volume or structural change. This may lead to some challenges for applications, as the material may break apart during field change, due to high internal stresses. A promising magnetocaloric material is La(Fe, Mn, Si)13Hy, where the transition temperature can be controlled through the Mn amount. In this work we use XRD measurements to evaluate the temperature dependence of the unit cell volume with a varying Mn amount. The system is modelled using the Bean-Rodbell model, which is based on the assumption that the spin-lattice coupling depends linearly on the unit cell volume. This coupling is defined by the model parameter η, where for η > 1 the material undergoes a first order transition and for η  ≤ 1 a second order transition. We superimpose a Gaussian distribution of the transition temperature with a standard deviation σ T 0 , in order to model the chemical inhomogeneity. Good agreement is obtained between measurements and model with values of η  ∼ 1.8 and σ(T0) = 1.0 K

Is the dynamics of open quantum systems always linear?

We study the influence of the preparation of an open quantum system on its reduced time evolution. In contrast to the frequently considered case of an initial preparation where the total density matrix factorizes into a product of a system density matrix and a bath density matrix the time evolution generally is no longer governed by a linear map nor is this map affine. Put differently, the evolution is truly nonlinear and cannot be cast into the form of a linear map plus a term that is independent of the initial density matrix of the open quantum system. As a consequence, the inhomogeneity that emerges in formally exact generalized master equations is in fact a nonlinear term that vanishes for a factorizing initial state. The general results are elucidated with the example of two interacting spins prepared at thermal equilibrium with one spin subjected to an external field. The second spin represents the environment. The field allows the preparation of mixed density matrices of the first spin that can be represented as a convex combination of two limiting pure states, i.e. the preparable reduced density matrices make up a convex set. Moreover, the map from these reduced density matrices onto the corresponding density matrices of the total system is affine only for vanishing coupling between the spins. In general, the set of the accessible total density matrices is nonconvex.Comment: 19 pages, 3 figures, minor changes to improve readability, discussion on Mori's linear regime and references adde

Digitalizador 3D para imagens antropométricas do pé

Este artigo apresenta um sistema de hardware e software para extrair medidas de pés da população brasileira. Sabe-se que os pés são diferentes, dependendo de diversos fatores como sexo, idade, raça, etc. Atualmente, pouco se tem levado em consideração estas diferenças no processo de construção do calçado brasileiro. A idéia é, colher uma imagem plantar do pé através de um scanner e ao mesmo tempo cinco imagens laterais através de uma câmera giratória. A partir destas imagens obter medidas de interesse e usando da técnica de triangularização gerar um modelo do pé em 3D, que possibilitará a confecção de formas de calçados na exata medida do pé.In this paper hardware and software systems is present to acquisition to feet anthropometrics measurements of Brazilians people. It knows itself that the feet are different, depending on diverse factors as sex, age, race, etc. This work consists of acquisition of plantar foot image with sensor type horizontal scanning and webcam to lateral image turn off foot. Within these images obtain measures of interest using to technical of triangularization to create a 3D model of foot.Red de Universidades con Carreras en Informática (RedUNCI